New aspects of the microhardness of ultraoriented polyethylene

Calleja, F. J. Baltá; Rueda, Daniel R.; Porter, Roger S.; Mead, W. T.

doi:10.1007/bf00551744

Cited by 44 publications

(10 citation statements)

References 14 publications

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“…The level of interest in the microindentation hardness (MH) of semicrystalline polymers has, especially during the last decade, given rise to a series of investigations [1][2][3][4][5][6][7] relating this mechanical property to changes in microstructure. Static indentation involves the formation of a permanent surface impression (typically a few microns in depth).…”

Section: Introductionmentioning

confidence: 99%

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

Calleja

Kilian

1988

Colloid & Polymer Sci

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Abtract:The application of thermodynamics of eutectoid copolymers and a generalized Tabor-rehtion to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by resuks on mek-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despke being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries ("meso-crystals") which yield cooperatively.

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Section: Introductionmentioning

confidence: 99%

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

Calleja

Kilian

1988

Colloid & Polymer Sci

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“…[31][32][33] In the present case, the distribution of fiber within the copolymeric matrix seems to be quite uniform, being the standard deviations lower than 6%. If we had important inhomogeneities in the samples, those regions rich in fibers will exhibit a significantly higher MH value.…”

Section: Viscoelastic Behaviormentioning

confidence: 78%

Influence of the Type of Fiber on the Structure and Viscoelastic Relaxations in Composites Based on a Metallocenic Ethylene-1-octene Copolymer

Cerrada

Benavente

Zamfirova

et al. 2002

Polym J

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ABSTRACT:Several composites of a copolymer of ethylene and 1-octene, synthesized with a metallocene catalyst, have been prepared with a 5% in weight of different types of fiber. The effect of the fiber on the crystalline structure and on the viscoelastic response is analyzed. The role of the fiber on crystallite development is discussed based on WAXS, SAXS, optical microscopy and DSC experiments. The viscoelastic behavior is modified by incorporation of the fiber when compared with the plain copolymer. Thus, both the intensity and location of the γ, β and α relaxations are dependent on the introduction of the fiber. The β relaxation is assigned to the glass transition temperature, in agreement with the calorimetric results (DSC and MDSC) in the copolymer. Moreover, the stiffness is increased in the composites above the glass transition temperature of the copolymer, allowing the analysis of the viscoelastic behavior up to temperatures well inside the melting region of the copolymer crystals, and thus enlarging substantially the service temperature of these composites.KEY WORDS Ethylene-1-octene Copolymer / Glass Fiber / Kevlar R Fiber / Nomex R Fiber / Crystallinity / Diffraction Patterns / Relaxation Processes / The use of metallocene catalysts has allowed a very rapid development in the field of polyolefins. These catalysts present single-site characteristics (and very high activities) and thus all the sites produce nearly the same chain architecture, 1 leading to polymers with narrow molecular weight distributions, and, in the case of copolymers with α-olefins, the side branches are randomly distributed in the polymer backbone. If the comonomer content is high enough, around 4 mol% depending upon the catalyst system used, a material exhibiting dual characteristics of plastic and elastomeric behavior can be achieved.An enhance of the mechanical and thermal properties required for load bearing engineering applications can be achieved by the incorporation of disperse fibers into polymers. This change in the mechanical and thermal behavior is due to several factors, such as variation in the mobility of the macromolecules in the boundary layers, the orientation influence of the fiber surface, the different types of fiber-polymer interactions, as well as the effect of fibers on the structure of the polymers. 2, 3 Glass fibers are probably the most common of all reinforcing fibers for polymer matrix composites. Their principal advantages are their low cost and high strength. Kevlar R is one of the most important manmade organic fibers ever developed. Fibers of Kevlar R consist of long molecular chains produced from polyparaphenylene terephthalamide. The chains are highly oriented with strong interchain bonding leading to a unique combination of properties, making them very useful in a wide variety of industrial applications. Other kind of reinforcement frequently used are fibers of Nomex R that inhere in long rigid molecular chains produced from polymetaphenylene diamine. They do not flow or melt upon heating, provid...

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“…It is of extreme importance also to compare those results with the ones obtained for isotropic polymer samples [18,21].…”

Section: Resultsmentioning

confidence: 99%

“…At least three different loads for each sample were used that verifies the above condition, ranging from 0.147°N to 2.942°N. This was necessary during the microindentation measurement to make sure the value of P d 2 was maintained constant and to correct for the instantaneous elastic recovery of the polymer at high temperatures if necessary [18].…”

Section: Microhardness Measurementsmentioning

confidence: 99%

Microindentation technique as a tool for investigating the development of order in PET under uniaxial stress

Abou-Kandil¹,

Flores²,

Calleja³

et al. 2008

J Polym Res

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The development of microhardness during annealing was used as a tool to follow the development of the liquid crystalline transient mesophase during the crystallization of uniaxially oriented polyethylene terephthalate (PET). 2D X-ray diffraction was used to characterize the different stages of the crystallization process. We were able to separate those stages by quenching into air. Microindentation hardness experiments were done in real time where samples were heated with their ends fixed on a specially developed stage and microhardness was measured simultaneously. The oriented samples examined exhibit a clear difference in behavior from isotropic samples that mainly lack the existence of such an ordered mesophase. The mesophase clearly has a reinforcement effect on the whole polymer matrix that leads to an increase in hardness value with annealing of the oriented PET films. Microindentation hardness is shown to be a versatile tool to detect the existence of the liquid crystalline transient mesophase. It is also efficient in comparing and explaining results obtained by wide angle X-ray scattering.

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New aspects of the microhardness of ultraoriented polyethylene

Cited by 44 publications

References 14 publications

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

Influence of the Type of Fiber on the Structure and Viscoelastic Relaxations in Composites Based on a Metallocenic Ethylene-1-octene Copolymer

Microindentation technique as a tool for investigating the development of order in PET under uniaxial stress

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